1. Field of the Invention
The present invention relates to improvements in a hydraulic pressure supply apparatus, and more particularly to a hydraulic pressure supply apparatus which includes a variable displacement pump and an accumulator.
2. Description of the Prior Art
JP-A-59-151601 discloses a hydraulic circuit which controls discharge pressure of a pump to a value slightly higher than a load side pressure detected by a pressure sensor. Due to this control, the pump is operated to decrease its power loss while supplying a proper pressure to the load side. Furthermore, in order to improve the pump in size and weight while further improving the power loss of the pump, another hydraulic circuit has been proposed. Such a hydraulic circuit is disclosed in JP-A-60-176737 wherein the hydraulic circuit includes an accumulator to a supply conduit which communicates a pump and a load side such as a hydraulic cylinder. The accumulator is operated to supply working fluid to the load side when the load side requires a flow rate which is greater than a maximum flow rate by the pump. With this conventional circuit, when the load side requires a small flow rate, the pump supplies all fluid required in the load side. When the load side requires a great flow rate, the accumulator supplies fluid to the load side in addition to the supplement by the pump.
However, in the event that the load side requires a large flow rate, the pump is increased in its discharge flow rate and simultaneously supplies fluid to the accumulator for charging since the above-discussed accumulator is always communicated with the pump. This degrades performance of the system in the supplying operation of working fluid to the load side.